The present invention relates to a vehicle seat assembly, and in particular to a vehicle seat assembly which is adapted to prevent a vehicle occupant from slipping forward under a seat belt in case of an impact such as a vehicle crash.
In a phenomenon conventionally known as the submarine phenomenon, a vehicle occupant slips forward under a seat belt in case of an impact such as a vehicle crash, thereby causing the hip belt to dislodge from the hip bone of the vehicle occupant. This phenomenon tends to occur when the vehicle occupant sits on the front edge of the seat or when the seat back is tilted rearward, and could diminish the effectiveness of the seat belt in restraining the vehicle occupant because the seat belt is dislodged from the proper part of the vehicle occupant which is suited for restraining the vehicle occupant.
In view of such a problem, it is conceivable to provide a projection in a front part of the seat frame, and install a panel in a front part of the seat to raise the front end thereof However, such a projection or a panel is too low to be effective and too high to provide desired sitting comfort.
There have been various proposals. For instance, U.S. Pat. No. 5,340,185 discloses a seat assembly using a wire and pulley arrangement for converting a forward movement of the seat in case of a vehicle crash into a lifting movement of the front edge of the seat. This arrangement uses the inertia force as a power source for actuating the front edge of the seat, and is advantageous in not requiring any other power source. However, the arrangement is highly complex, and there would be considerable difficulty in achieving a successful design. Japanese utility model laid open publication No. 3-61440 discloses a similar seat assembly relying on a propellant as a power source for selectively raising the front edge of the vehicle seat. According to this arrangement, although it is necessary to restrain the vehicle occupant for a prolonged period of time depending on the situation, the seat front end will drop again after the thrust of the propellant actuator is used up, and this prevents this prior art arrangement from being truly effective in preventing a submarine phenomenon.
An automobile is often equipped with an emergency locking retractor (ELR) which locks up a winding shaft for the seat belt in case of a sudden stop or a vehicle crash. An ELR device is capable of locking up the winding shaft in a very short time upon detecting a deceleration level greater than a prescribed value so as to prevent any further pay-out of the seat belt. However, simply locking up the winding shaft would not prevent a pay-out of a length of the seat belt corresponding to the tightening of the part of the seat belt wound on the winding shaft. According to a pretensioner device proposed in the U.S. Pat. No. 4,705,296, the buckle which is attached to an end of the seat belt is rapidly moved in the direction to tension the seat belt to enhance the restraining capability of the seat belt. Also, to prevent the buckle from moving backward immediately thereafter, the pretensioner device is provided with a reversing preventing device such as a ratchet and a one-way clutch, separately from that of the ELR device.
The inventors of this application have realized that such a pretensioner device is typically provided with a power unit for pulling the buckle powered by high pressure gas produced from a chemical reaction, for instance, as was the case with the invention disclosed in Japanese patent laid open publication No. 10-181529 by the same applicant.
In view of such problems of the prior art, a primary object of the present invention is to provide a vehicle seat assembly which provides a sitting comfort under normal condition, but can prevent a submarine phenomenon in a reliable manner.
A second object of the present invention is to provide a vehicle seat assembly which is simple in structure so as to allow a high level of flexibility in layout.
A third object of the present invention is to provide a vehicle seat assembly which is economical to manufacture.
A fourth object of the present invention is to provide a vehicle seat assembly incorporated with both a pretensioner device and a submarine preventing device which requires a relatively small number of component parts and is suited for compact design.
According to the present invention, these and other objects can be: (1) a slip preventing member supported by a fixed part of a seat so as to be pivotable between a retracted position and a raised position; (2) an actuator interposed between a fixed part of the seat and a part of the slip preventing member, and adapted to move the slip preventing member toward the raised position; and (3) a lock mechanism for retaining the slip preventing member at the raised position then one embodiment, the slip preventing member includes a lever member supported by a fixed part of the seat so as to be pivotable around a laterally extending pivot shaft, and a rod member extending along the front edge of the seat and attached to a free end of the lever member.
Thus, the present invention provides both a favorable sitting comfort under normal condition and a reliable operation in case of a high impact situation. The simple arrangement contributes to the economy, compactness and reliability of the arrangement. According to a particularly preferred embodiment of the present invention, the slip preventing member comprises a pair of lever members supported on either side of the seat by a fixed part of the seat so as to be pivotable around a laterally extending pivot shaft, and a rod member extending along a front edge of the seat and attached across free ends of the lever members. In particular, at least one of the lever members preferably consists of a bell crank having a first end attached to the rod member, and a second end adapted to be actuated by the actuator which typically consists of a piston/cylinder arrangement including a propellant.
The lock mechanism may be selected from a number of possible arrangements such as (1) a one-way lock mechanism provided around the pivot shaft, and (2) a one-way lock mechanism incorporated between a piston rod and the cylinder.
The submarine preventing arrangement is preferably combined with a pretensioner for full protection of the vehicle occupant, and they are normally placed adjacent to each other. It is advantageous to use a common actuator. For instance, the pretensioner device may include a bell crank member which is pivotally supported by a fixed part of the seat so as to be pivotable around a pivot shaft extending laterally with respect the seat. The bell crank member has a first end attached to the buckle, and a second end attached to an end of the actuator which is common to the submarine preventing arrangement.